DESCRIPTION (Verbatim from the Applicant): Degenerative changes in the wrist are believed to be the result of alterations in the anatomy and kinematics of the carpus after traumatic injury. With NIH funding (R29 AR44005), over the past five years we have developed a novel, non-invasive CT image-based technique to study three-dimensional (3-D) carpal bone motion in vivo. We have used this technique, which we call markerless bone registration (MER), to study carpal bone motion in young, healthy individuals, and in injured patients who had scapholunate interosseous ligament (SLIL) tears. This proposal builds on our current findings. We have determined that wrist flexion, extension, ulnar deviation and radial deviation in young, healthy individuals are each accomplished by unique patterns of carpal bone motion, and that carpal kinematics differs slightly in males and females. We have also found abnormalities in both carpal bone posture and kinematics in patients with SLIL tears. In this proposal we will extend our investigation into the mechanism by which the individual carpal bones contribute to wrist motion by exploring motions beyond flexion-extension and radio-ulnar deviation, and by studying the effects of age and gender. Our first aim is to determine 3-D carpal bone motion for the complete range of motion of the wrist. We hypothesize that the patterns of carpal bone motion will differ in each direction of wrist motion. Our second and third aims are to compare the carpal kinematics in elderly and young individuals, and to determine whether there are differences in carpal bone shape in males and females. We hypothesize that carpal bone motion will not differ with age, and that carpal bone shape will not differ significantly between males and females. In our fourth and fifth aims we will explore the effect of SLIL tears on intercarpal joint space and we will investigate the kinematic effects of scaphoid nonunion. We hypothesize that SLIL tears will alter the joint space in patients with SLIL tears, and that proximal scaphoid nonunions will affect the kinematics of the surrounding carpal bones more than distal scaphoid nonunions. The Specific Aims of this proposal are focused in two areas: first to test hypotheses and expand the knowledge base regarding normal carpal mechanics, and second to further explore the kinematic implications of common wrist pathologies (SLIL tears and scaphoid nonunions). The results of our work will broaden the understanding of carpal function and provide the basis for further studies on cartilaginous and ligamentous tissues. Our goal is to generate information that will improve the evaluation, diagnosis and treatment of wrist injury.